This invention relates to thermostatic heater apparatus and more particularly to submersible thermostatic heater apparatus employing an electronic thermostat.
Thermostatic heater apparatus intended for aquarium applications normally take the form of an electrical resistance heater controlled by a thermostat. The electrical resistance heater typically is configured as a resistance wound on a ceramic or glass former where the resistance winding per se takes the form of a coil sitting in a threaded groove in the ceramic former, or a coil mounted within a longitudinal groove. Other variations include a coil of wire held in glass tubes or straight lengths of wire disposed on a glass tube or other support.
Many forms of thermostatic heater apparatus utilized for aquarium applications employ bimetal elements for the thermostats since this form of thermostat tends to be significantly less expensive. However, a difficulty encountered in using bimetal elements in these applications tends to be that the same are highly accurate only at the calibration temperature thereof while displaying marked deficiencies through the remainder of the adjustable range. In addition electrical contacts actuated by the bimetal elements are prone to fusing after extended periods of use.
In form, the thermostatic heater apparatus heater apparatus utilized for aquarium applications may comprise an integrated unit wherein a glass tube includes both the heater element and the thermostat. Combined units of this type are often submersible; however, sensing temperature and heating through the glass side or base of the aquarium in non-submersible units is often utilized. A typical example of a submersible, combined unit is disclosed in European patent application No. 0228521 published July 15, 1987.
Alternatively, separate thermostat and heater configurations may be employed. In such separate units, the heaters are typically provided encased in glass or metal tubes for submersion in the aquarium, or as pads which are placed externally under or at the sides of the aquarium tank. With an independent heater, a separate thermostat which is submersible or is external and senses temperature through the glass is typically employed. The separate thermostat frequently employs a dial-like indicating device for indicating temperature and/or providing adjustment. Such indicating arrangements tend not to have substantial visual appeal and are often regarded as unsightly. This is a distinct disadvantage since frequently, a major purpose of an aquarium is a visually appealing display.
Therefore, it is a principal object of this invention to provide improved submersible thermostatic heater apparatus manifesting highly accurately operation throughout an adjustable range, a pleasing appearance and a combined design.
Various other objects and advantages of the present invention will become clear from the following description of an exemplary embodiment thereof and the novel features will be particularly pointed out in conjunction with the claims appended hereto.